The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Electronic parking brakes are now commonly employed on various motor vehicles such as cars and light trucks. Typically the electronic parking brake activates the brakes on the rear wheels of the vehicle when it is engaged. Some present day vehicles use the electronic parking brake to assist the driver of the vehicle during hill-start situations. With a hill-start situation, the hydraulic brakes of the vehicle may be programmed to remain active for a calibratable amount of time, and then the electronic parking brake may be automatically engaged to provide additional braking action during the hill-start maneuver.
The effectiveness of the electronic parking brake in either hill-start situations or in simply holding the vehicle stationary while the vehicle is parked, can be somewhat reduced when the vehicle is parked on a hill with a moderate or steep grade or the rear axle is located on a lower friction surface (ex: gravel, snow, ice). This is particularly so if the vehicle is orientated on a decline, that is with the front axles of the vehicle at an elevation which is lower than the rear end of the vehicle. In this instance the weight of the vehicle may biased significantly toward the front end of the vehicle, and thus well less than 50% of the vehicle's weight may be present on the rear wheels of the vehicle. As a result, the electronic parking brake, which is engaging the brakes on the rear wheels, may be limited in effectiveness due to the reduced weight that the tires at the rear end of the vehicle are experiencing. In this example, if the vehicle has an all wheel drive (“AWD”) system, there ordinarily would not be any counteracting torque applied to the front axles of the vehicle while the electronic parking brake is engaged. But being able to use the vehicle's AWD system to apply a counteracting torque to the front axles of the vehicle would significantly enhance the ability to hold the vehicle stationary, especially when the vehicle is parked on a decline with its front end lower than its rear end or the rear wheels are located on a lower friction surface (ex: gravel, snow, ice). The use of the vehicle's AWD system to apply a counteracting torque to the front axles (or possibly to all axles) of the vehicle during an emergency braking operating could also be highly beneficial in augmenting the vehicle's electronic parking brake's antilock braking function in bringing the vehicle to a rapid and controlled stop.